3,6-Dichloro-2-methoxybenzoic acid (also known by its common name dicamba) is a highly effective and commercially important herbicide that is useful for controlling a wide variety of unwanted vegetation, including agricultural weeds. Convenient and economical methods of preparing dicamba, therefore, are of significant commercial importance.
A number of synthetic routes for the preparation of dicamba have been reported in the literature. One reported route proceeds through a 2,5-dichlorophenol intermediate as illustrated in Scheme 1 below:
See, e.g., U.S. Pat. No. 1,161,611.
Another reported route proceeds through either a 4-bromo-3,6-dichloro-2-(hydroxymethyl) phenol intermediate or a (3-bromo-2,5-dichloro-6-methoxy-phenyl)methanol intermediate as illustrated in Scheme 2 below:
See, e.g., U.S. Pat. No. 3,928,432.
Still other reported routes employ starting materials, or proceed through intermediates, such as 2,5-dichlorophenol (see, e.g., U.S. Pat. No. 4,232,172); 2,5-dichloro-4-bromophenol (see, e.g., U.S. Pat. No. 3,728,403); 1,2,4-trichlorobenzene (see, e.g., U.S. Pat. No. 3,013,054), 2,3,6-trichlorobenzoic acid (see, e.g., U.S. Pat. No. 3,444,192); or 2,6-dichlorobenzonitrile (see, e.g., Romanowski et al., Prezem. Chem. 54(1), pp. 26-31 (1975)).
As compared to currently known processes, however, the processes of the present disclosure provide one or more advantages in the large-scale manufacture of dicamba with respect to cost and/or availability of starting materials, throughput and/or required processing steps (such as hazardous processing steps and/or separation/purification steps), equipment requirements (such as high pressure and temperature reactors), reaction conditions, reaction times, yield, energy consumption, capital costs, and the like.